Rotary processing uses continuous agitation via a motorised drum or tube. Whether you're using a Jobo processor, a compact Rondinax, or a DIY motor setup, rotary development offers extreme consistency — but requires understanding how it differs from manual inversion.
This guide assumes you've completed:
Active time: 20-30 minutes Total time: 1.5-2 hours (including drying)
Rotary processing requires understanding time adjustments and consistent technique, but is more forgiving than E-6 once you've calibrated your setup.
What is Rotary Processing?
In rotary processing, your developing tank sits horizontally and rotates continuously throughout development. This differs from manual processing where you periodically invert the tank.
The Key Difference
Manual inversion: Agitation happens in bursts. Chemistry settles between inversions.
Rotary processing: Constant, gentle agitation. Chemistry never settles.
This fundamental difference affects:
- Development times
- Contrast characteristics
- Chemistry requirements
- Reproducibility
Rotary processing can reduce development times by 10-30% compared to manual inversion due to the constant agitation maintaining fresh developer at the emulsion surface.
Equipment Options
Equipment Costs
| Equipment | Typical Price Range |
|---|---|
| Jobo CPE-2/3 | £200-400 used |
| Jobo CPP-2/3 | £600-1500 |
| DIY motor setups | £30-80 |
Jobo Processors
The gold standard for rotary processing:
Jobo CPP-3 / CPA-3
- Fully automated temperature control
- Lift mechanism for chemical changes
- Multiple drum sizes available
- Expensive but professional-grade
Jobo CPE-2 Plus
- Manual lift, but temperature controlled
- More affordable entry point
- Widely available used
Jobo 1500/2500 Series Tanks
- Can be rotated manually on a base
- Works with motorised rollers
Rondinax Daylight Tanks
Vintage daylight-loading tanks with built-in rotation:
- Load film in daylight
- Hand-crank or motor-driven rotation
- Compact and self-contained
- Sought-after and expensive when found
DIY Motor Bases
Budget rotary solutions:
- Jobo-compatible tanks on motorised roller bases
- Patterson tanks with 3D-printed adapters
- BBQ rotisserie motor conversions
- Purpose-built bases (Rondinax-style)
The motor speed matters. Too fast creates excessive turbulence and uneven development. Aim for 30-75 RPM — slow enough for smooth, laminar flow.
When Rotary Processing Excels
Colour Processes (C-41 and E-6)
Rotary is ideal for colour work because:
- Temperature consistency — Tank stays in tempered water bath
- Even development — Critical for colour balance
- Reproducible results — Same agitation every time
- Efficient chemistry use — Lower volumes required
Most professional labs use rotary processors for colour work.
Large Format Sheet Film
Rotary drums handle sheet film elegantly:
- Multiple sheets processed evenly
- No risk of sheets sticking together
- Consistent results across batches
- Expert drums available for 4x5, 5x7, 8x10
High-Volume Processing
If you develop regularly:
- Set up once, process many rolls
- Walk away during development
- Consistent results roll after roll
- Less physical effort than manual inversion
Adjusting Development Times
Continuous agitation increases effective development. You must compensate:
Time Reduction Guidelines
| Process | Manual Time | Rotary Adjustment | Notes |
|---|---|---|---|
| B&W standard | 100% | 70-85% | Film and developer dependent |
| B&W dilute | 100% | 80-90% | Less reduction for dilute developers |
| C-41 | 3:30 | 3:15 | Slight reduction at most |
| E-6 first dev | 6:00 | 5:45-6:00 | Minimal change, test first |
Never use published rotary times for manual processing or vice versa. The results will be significantly different. Always verify which agitation method a time chart assumes.
Finding Your Times
For black and white films without published rotary times:
Start with 75% of manual time. If manual development is 10 minutes, try 7:30 for rotary.
Evaluate the negatives. Too dense? Reduce further. Too thin? Increase slightly.
Adjust in 5-10% increments. Small changes have noticeable effects with constant agitation.
Document your findings. Once you find the right time, it will be consistent.
Chemistry Considerations
Volume Requirements
Rotary processing typically uses less chemistry per roll:
- Jobo minimum: 135-270ml per roll depending on drum size
- Manual tanks: Usually 300-500ml per roll
The drum design ensures chemistry covers the film despite lower volumes — but only while rotating. Never let a partially-filled drum sit stationary.
One-Shot vs Replenishment
One-shot recommended for rotary because:
- Exact same chemistry strength every time
- No tracking of roll count
- No replenishment calculations
- Simpler workflow
Replenishment systems can work but require:
- Careful tracking of total area processed
- Precise replenishment ratios
- Understanding of system capacity
For colour processing (C-41/E-6), one-shot simplifies everything. The consistency is worth the slightly higher chemistry cost.
Developer Oxidation
Rotary processing can accelerate oxidation:
- More air contact during rotation
- Foam can form on some developers
- Partially-used working solutions may not keep well
Use fresh chemistry for best results. Don't try to reuse working solution that's been rotated.
Temperature Control
Why It Matters More
With constant agitation, temperature variations have immediate effects:
- No "averaging" from settling chemistry
- The film sees current temperature constantly
- Colour processes are especially sensitive
Maintaining Temperature
Water bath method:
- Drum rotates in tempered water
- Processor controls water temperature
- Most Jobo systems work this way
Pre-heating only:
- Heat drum and chemistry before processing
- Monitor temperature throughout
- Less precise, requires attention
Room temperature:
- Acceptable for B&W at 20°C
- Not recommended for colour processes
- Still benefits from pre-tempering
For C-41 at 38°C, a proper temperature-controlled processor is almost essential. The 3:30 development time is too short to tolerate drift.
The Rotary Processing Workflow
Setup
Prepare chemistry. Mix and bring to temperature 15-20 minutes before processing.
Pre-heat the drum. Fill with water at process temperature, rotate briefly, then drain.
Load film. In darkness for standard tanks, or daylight for daylight-loading systems.
Verify temperature. Check chemistry temp immediately before starting.
Processing
Pour developer quickly. Start rotation and timer simultaneously.
Maintain continuous rotation. The drum should never stop during development.
Drain efficiently. Most drums have a pour position. Drain into the last 10-15 seconds of step time.
Proceed through remaining steps. Stop/wash, fix (or blix for colour), wash.
Best Practices
- Don't stop rotation mid-step. Even a brief pause can cause uneven development marks.
- Use consistent rotation speed. Changing speed mid-roll affects results.
- Pour quickly. Slow pours mean uneven development start across the roll.
- Practice the drain. Efficient draining is crucial for timing.
Rotary vs Manual: Results Comparison
Tonality and Contrast
Rotary processing tends to produce:
- Slightly higher contrast than equivalent manual processing
- More pronounced grain (due to increased development activity)
- Very even development across the frame
- Consistent edge-to-edge density
Manual processing allows:
- Lower contrast (with reduced agitation)
- Compensation effects (stand/semi-stand)
- Slightly finer grain appearance
Consistency
Rotary wins decisively:
- Human agitation varies, motor agitation doesn't
- Temperature maintenance is easier
- Results are reproducible year after year
Convenience
Rotary:
- Less hands-on time
- Walk away during processing
- Higher setup cost
- Requires specific equipment
Manual:
- No special equipment needed
- More tactile, hands-on process
- Lower cost
- Works anywhere
Common Issues and Solutions
Uneven Development
Cause: Air bubbles trapped during pour or insufficient rotation speed.
Solution: Tap drum firmly after pour. Ensure rotation speed is adequate (50+ RPM). Use a pre-soak to wet the emulsion first.
Surge Marks
Cause: Speed too high or inconsistent, causing turbulent flow patterns.
Solution: Reduce rotation speed. Ensure motor runs smoothly without stuttering.
Bromide Drag (Streaks)
Cause: Usually from rotation in only one direction.
Solution: Use reversing rotation if available. Most quality processors alternate direction.
Inconsistent Density Roll-to-Roll
Cause: Chemistry exhaustion, temperature drift, or timing variations.
Solution: Use fresh one-shot chemistry. Verify temperature before each run. Use a precise timer.
Building a DIY Rotary Setup
For those interested in rotary processing without Jobo prices:
Basic Requirements
- Motor: Low RPM (30-75), reversing preferred
- Roller base: Two parallel rollers that drum sits on
- Tank: Jobo drums work well, Patterson with adapters possible
- Temperature control: Water bath or sous vide circulator
Simple Approach
Get a Jobo 1500 series drum. Available used, works on any roller base.
Build or buy a roller base. Can be as simple as two dowels on a motor.
Add a water bath. A plastic container the drum can sit in while rotating.
Control temperature. Sous vide circulator maintains water bath temperature.
DIY setups require testing. Process a test roll and check for evenness before committing important film. The specific speed and direction matter.
Is Rotary Processing Right for You?
Consider rotary if:
- You process colour film (C-41 or E-6) regularly
- Consistency is paramount
- You're willing to invest in equipment
- You process large format sheet film
- You want hands-off processing time
Stick with manual if:
- You only process occasionally
- You enjoy the hands-on ritual
- You want to use stand or semi-stand techniques
- Budget is a primary concern
- You process primarily black and white
Rotary processing isn't better or worse than manual — it's a different approach with different strengths. The best choice depends on what you shoot, how often you process, and what you value in the darkroom experience.